In the prior art, various devices have been proposed for tensioning flexible drive belts such as chains or the like. U.S. Pat. No. 4,068,535 to Sheets discloses such a device that includes a first idler assembly for engaging the slack run of a drive belt and a second idler assembly for engaging the drive run of the belt. Tensioning members are provided for adjusting the distance between the first idler assembly and the second idler assembly to a distance sufficient to cause the apparatus to maintain a position between the drive pulley and the driven pulley.
U.S. Pat. No. 2,963,918 to Blakstad discloses another chain or belt tensioning device wherein the device is arranged between the runs of the chain or belt. In this device, spring-influenced plungers cooperate with the two runs of the chain or belt for tensioning. The device is designed to be mounted to a surface adjacent the runs.
U.S. Pat. Nos. 4,662,862 and 4,798,562 to Matson and Matson et al. disclose other examples of tensioning devices. In the Matson patent, straps and engagement means are used to secure the tensioning members a select distance away from one another by means of a ratchet-like mechanism. The mechanism is arranged so that the force required to move the tensioning members toward one another is smaller than the force required to move the tensioning members away from one another. The Matson et al. patent also uses straps and positioning devices. The straps are perforated so as to align with posts in the tensioning members for spacing adjustment.
The devices noted above are not without their disadvantages. The Blakstad tensioner requires a surface adjacent the runs of the belt or chain. Adjusting the spacing in the Matson et al. and Matson devices is tedious due to the use of the perforated straps. Further, this device lacks any biasing means associated with the tensioning members to accommodate fluctuations in the belt or chain.
While the Sheets device is free-floating and uses springs as part of the device, this construction is rather complicated. Moreover, since Sheets uses pulleys to guide the drive elements, one or more of the drive elements can easily be displaced from the pulleys during movement.
In light of the deficiencies in prior art tensioning devices as discussed above, a need has developed to provide an improved tensioning device. In response to this need, the present invention provides an improved tensioning device which is free-floating, easily adjusted and capable of accommodating fluctuations in the drive runs of a flexible drive member.